(i) Field of the Invention
The present invention relates to an exhaust gas purifying catalyst that removes toxic substances contained in exhaust gas from an internal combustion engine of an automobile, a motorcycle, and others.
(ii) Background Art
A variety of catalysts for purifying exhaust gas emitted from an internal combustion engine of an automobile and the like have been provided. These days, most of the catalysts are three-way catalysts that purify HC, CO, and NOx at the same time. Such catalysts are disclosed, for example, in Publication of Unexamined Japanese Patent Application No. Hei 3-196841, Publication of Unexamined Japanese Patent Application No. Hei 5-23593 and Publication of Unexamined Japanese Patent Application No. 2001-259424.
In one example of the three-way catalyst, one of or a combination of catalytic components, such as Pt, Pd and Rh, is dispersed in and carried by a refractory inorganic compound powder, such as alumina and ceria-zirconia, to form a catalytic composition. Then the catalytic composition is applied to cover a honeycomb substrate made of cordurite, metal and the like.
In another example of the three-way catalyst, a honeycomb substrate made of cordurite, metal and the like is covered with a refractory inorganic oxide, such as alumina and ceria-zirconia, and is soaked in a slurry containing one of or a combination of catalytic components, such as Pt, Pd and Rh, so as to carry the catalytic components.